In harvesting of a standing crop, it is well known that the efficiency and speed of the combine harvester, when using a straight cut header, or the swather can be improved by reducing the length of the straw cut with the head of the crop. Many farmers have therefore obtained this improvement in efficiency by raising the header above a normal cutting height which provides an increase in speed, more efficient threshing, lower fuel consumption, lower repair bills and a reduction in the likelihood of picking up a rock.
The problem with this technique in harvesting is that the standing stubble left by the combine is of a height greater than can be accommodated by the subsequent cultivation and seeding tools.
Various alternatives are available for handling the standing stubble. One alternative involves using a swather to cut the stubble after the combine has been through the field but this technique leaves windrows of the cut straw which would need to be burnt, which is an unacceptable, unsustainable and environmentally unfriendly way to farm. It is also possible to operate the swather with the canvasses removed to avoid windrowing of the straw. However this does not operate effectively as the straw will not flow over the obstructions incorporated in the conventional design of the swather.
It has been tried simply to work the stubble into the ground through separate tillage operations but due to the length of the stubble this causes plugging of the machine and often leaves lumps or piles of the straw throughout the field.
Yet further techniques available in the industry involve the use of rotary and flail mowers which simply chop the straw into relatively small pieces but these machines are relatively expensive to purchase, require high horse power to drive are relatively slow in operation as they are narrow and have low ground speed capability.
A further proposal which has been set forth in patents but is not commercially available is shown for example in U.S. Pat. No. 2,401,513 (Schmidt) which discloses a second cutter behind the combine header which cuts the straw at or adjacent ground level. U.S. Pat. No. 3,399,517 (Magee) discloses a combine harvester header with two knives at the forward end for use in harvesting a corn crop.
The use of the single cutter bar behind the header cutter bar causes the straw to be cut basically into three pieces. The first upper piece is the piece carrying the head of the crop which is carried into the combine harvester. The remaining standing stubble is then cut only into two pieces, one of which is left standing and attached to the ground and the other of which is cut and discharged onto the ground.
Single sickle knife cutters are available, for example that manufactured by Muchka of Alberta Canada which provides a single knife of only 30 feet in width in a pull behind arrangement which can be used to cut down the standing stubble. However these arrangements are of limited width and again can only cut the stubble into a separated piece and standing piece.
It is generally accepted that straw pieces either standing or cut on the ground should not exceed the shank spacing on the following tillage machine. In many recent tillage machines, 8 inches is the narrowest shank spacing and often it is difficult with the above techniques to obtain straw pieces of less than 8 inches while maximizing the efficiency of the combine harvester.